How far out of the way should you drive to save at the pump? Sites like GasBuddy allow drivers to look up prices in their area, and detour to the cheapest source.
Let's say that a driver wants 15 gallons of gas. If the price difference between two stations is 30c per gallon, which is unusually high, this works out to $4.50. How far does it make sense to drive even for this high savings? If the driver averages about 10 miles an hour, with lights and traffic, then even two miles out of the way will take 24 minutes of driving time, and will consume, assuming 20 MPG, a fifth of a gallon of gas, or 60c at $3 gas. So, for a net savings of $3.90, our hypothetical driver has lost almost half an hour. And that's if the price differential is very high.
What about for a 5c/gallon difference? For a 15 gallon purchase, the savings is only 75c. If we assume that our driver's time is worth $10 an hour, this savings justifies a detour of no more than 4.5 minutes, total.